JP2003-81042 A discloses a parking assisting apparatus comprising a first sensor for measuring a distance with respect to an obstacle in a lateral direction of the vehicle, a second sensor for measuring a travel distance of the vehicle, a yaw angle detector for detecting a yaw angle of the vehicle, guiding means for outputting guidance information as to operations of the vehicle to a driver, and a controller configured to estimate an initial stop location based on measurements of the distance and the travel distance obtained in the course of moving the vehicle forward toward the initial stop location, and provide the driver with timing information suited to start to move the vehicle backward for parking via the guiding means based on measurements of the yaw angle and the estimated initial stop location.
Further, JP2003-270344 A discloses a technique for determining a target orientation of the vehicle to be implemented at parking by obtaining distance information between the vehicle and another parked vehicle using distance-measuring sensors such as a sonar sensor or the like, detecting parking space available for parking based on the obtained distance information, detecting a side of another parked vehicle adjacent to the detected parking space, and determining the target orientation based on the detected side of the other parked vehicle such that the side of the vehicle within the parking space will be parallel to the detected side of the other parked vehicle.
By the way, there is a stage as a pre-parking stage in which the driver moves the vehicle toward a parking start position. In this stage, the driver generally tends to move the vehicle toward the parking start position after driving the vehicle near the desired parking space. At this time, if the system can estimate the orientation of the parking space, it is possible to start to perform a parking assist (for example, a parking assist for the stage in which the driver moves the vehicle toward the parking start position) in an earlier stage using the estimated orientation. However, there are many travel patterns of the vehicle near the parking space. For example, there is a case in which the driver moves the vehicle in such a manner that the vehicle passes in a slanting direction with respect to the front side of the parking space. Thus, with a simplified configuration, it is difficult to precisely estimate the orientation of the parking space.